8 Accelerator Engineering and Technology: Accelerator Technology
443
Fig. 8.61 Schematic of a Modern DCCT. The two cores on the right form the “zero flux” DCCT,
while the left hand core is an AC transformer that extends the bandwidth of the system to higher
frequency
current loop (Fig. 8.61). Once the compensation current and the beam current are
identical the net static magnetic field seen by the toroids is zero (hence zero flux)
and the output from the demodulator is also zero. The beam current is then simply
obtained by measuring the voltage produced by this compensation current across a
known resistor. For modern DC transformers such a zero flux detector is combined
with an AC transformer. The AC transformer is used to feedback on fast changes
which are not compensated by the DC transformer and hence significantly increases
the bandwidth of the system, allowing measurement from DC to a few MHz.
8.6.3 Diagnostics of Transverse Beam Motion
The instrumentation used to look at transverse beam motion is very important for the
efficient operation of any circular accelerator [128]. There are three main parameters
that can be measured using such diagnostics: the betatron tune, chromaticity and
coupling.